Olive, hang in there. I keep telling myself that life is not fair. We did nothing to deserve to go through this. Having said that, this is life. I heard a phrase before, "If it does not kill you, it will make you stronger". This is life's way to make you stronger. you have become a strnger person, and in my case, I can certainly see things better from other people's perspective. Can't tell if OW gets it all, or not. Regardless, that's her life. If she is so lucky, that's her fortune. I know I won't be strong enough to wish them luck, but I have, at one point, came to the conclusion that if that's the way it is, I will cherish the years that I had with H and if he is meant to leave and have a "better" life (or not) with someone else, I will continue to make my own life better.
The part wtih your daughter is tough. She will know and see that you are her support. I personally would not let OW and H spend time with D before the D until it is finalized. That's just me because I don't want to confuse them to see that it's OK to date before D is final. It may not be possible in your sitch, (don't know how H will react).
Good to hear from you again. I have been thinking about you. Take care.